1. Field of the Invention
The present invention relates to apparatus and methods for diagnosing, quantifying, and correcting for human central auditory nervous system (CANS) impairment, and in particular binaural phase time delay asynchrony.
2. Description of the Prior Art
Preliminary studies indicate an important connection between the binaural synchronization of the central auditory nervous system (CANS) and gross, fine and oral motor function. A binaural phase time delay (BPTD) is defined herein as a synchronization disruption (delay) in phase and time of the auditory input signals to the two ears. Two types of BPTDs have been defined by the investigators: pathological BPTDs which are “built-in” to a person's CANS, as is the case with a person with neurological injury or disease process, and clinical BPTDs which are induced in a person's CANS using an external device, to compensate for a pathological phase time delay.
A BPTD is a combination of a phase shift and a time delay. For pure tones, a specific phase shift results in a specific time delay. For example, at 1000 Hz a 180° phase shift results in a 0.5 ms time delay. However for speech and other multi-frequency sounds, one specific time delay would result in several different frequency-dependent phase shifts. Note that a time delay can be much larger than the maximum phase shift for a given frequency.
Operationally, binaural interaction of the CANS requires the two ears to integrate dichotic signals separated in time, frequency, and/or intensity. The brain stem is crucial for binaural interaction of acoustic stimuli. Stillman (1980) has emphasized that precise timing of excitatory and inhibitory inputs to each cell along the auditory pathway is critical if each cell is to respond in an appropriate manner. Oertel (1997) has also studied the effects of timing in the cochlear nuclei. The superior olivary complex is an important relay station of the ascending tract of the CANS and is critical for binaural listening capabilities. It is this cross correlation behavior of the two ears that afford the selective listening capability in noisy environments, and the ability to spatially localize sound sources. However, it has been shown that signals from the two ears must have synchronized arrival times for binaural cells to be activated in the superior olivary complex. A delayed signal from one ear negates a binaural response. There is evidence that the synchronization of auditory stimuli is important above the superior olivary complex, at the levels of the brainstem and cerebral cortex.
In individuals (adults and children) with an impaired CANS, a pathological BPTD has been observed between the two ears which is in some cases is quite large (15–20 msec). The pathological BPTD not only decreases speech intelligibility in complex listening environments, but also (somewhat surprisingly) degrades motor (gross, fine, oral) and visual performance. Furthermore, a clinically-induced BPTD, designed to compensate for the pathological BPTD in the subject, significantly improves the speech intelligibility, gross and oral motor function the subject.
It is well known that head injury frequently results in generalized trauma to the brainstem and to higher cortical mechanisms which include the central auditory nervous system, resulting in central auditory processing function abnormalities. Other conditions such as sensory integration problems, speech and language delays, hearing impairment, learning disabilities, multiple sclerosis, Parkinson's Disease, autism, stuttering, developmental delays, central auditory processing disorders, psychological disorders, and neurological disorders have been associated with CANS dysfunction. Individuals with central auditory processing problems often demonstrate difficulty comprehending and remembering auditory information. In addition, these individuals have particular difficulty attending to auditory information in the presence of auditory distractions.
In some traumatic brain injuries and other debilitative neurological brain disorders, the processing of information by the central auditory nervous system is impaired and affects comprehension and recall of auditory information. Operationally, the central auditory nervous system typically receives auditory information from both ears and integrates the input received, even though the acoustic signals received by the ears may be somewhat separated in time, frequency, and/or intensity. Such binaural integration by the central auditory nervous system may be substantially provided in the brain stem. Further, it has been observed that the precise timing of excitory and inhibitory inputs to cells of the central auditory nervous system can affect these cells' behavior to respond appropriately. In particular, it has been shown that auditory signals from both ears must have a relatively synchronized arrival time for certain binaural cells to be activated in the superior olivary complex. Thus, a delayed (e.g. millisecond) response from one ear can impair the integration of binaural response. This is not reflected in the function of the inner ear. However, an individual with a peripheral hearing loss may also have CANS dysfunction or a mechanical effect that creates a disruption of the synchrony between the two ears.
Behavioral and physiological (auditory brainstem response, middle latency response, cortical evoked potentials and mismatched negativity) methods have been employed to measure time parameters of the central auditory nervous system. Previous studies, however, have only analyzed the relationship of timing differences with respect to various pathologies (e.g. a latency in response has occurred). In particular, the development of tests quantifying the changes in auditory input between a subject's ears has been solely used as a diagnostic procedure for identifying a central auditory processing dysfunction. Since the anatomy of the brain stem indicates links between binaural signal processing and integration and motor control, it is not surprising that disorders of the central auditory nervous system often affect other functions such as sensory perception, integration, fine and gross motor, oral motor and visual processing. Accordingly, it would be useful to provide procedures and a diagnostic device that more accurately identify and quantify binaural processing disorders and the relationship of such disorders to other neurologically-based abnormalities. Further, it would also be useful to have a device that subjects manifesting binaural dysfunction-derived disorders can utilize to enhance day-to-day activities so that there may be enhanced speech understanding and recognition, concentration, gross motor movements (e.g. walking), fine motor movements (e.g. writing), oral-motor movement (e.g. speaking) or visual function.
The following references are relevant to the present invention:
U.S. Pat. No. 5,434,924 to Jampolsky; “Two New Methods for Assessment of Central Auditory Function in Cases of Brain Disease,” Matzker, Annals Of Otology, Rhinology, & Laryngology 68, 1185–1196, 1959; “Auditory and Vestibular Aberrations in Multiple Sclerosis,” Noffsinger et al, Acta Otolaryngologica, 303 (Suppl.), 1–63, 1972; “Assessing Central Auditory Behavior in Children,” Willeford, Central Auditory Disfunction, 43–72, 1977; and Westone style # 47 Soft PVC Custom Molded Ear Plug with Quiet Tech Int. Filter.
A need remains in the art for apparatus and methods for diagnosing, quantifying, and correcting for binaural phase-time delay asynchrony.